Summary
The query is looking for historic executions plans which used nested loop joins and producing a report that is attempting to produce some measures of work done by nested loops, showing the variation over time. In principal this could be a good thing as it allows us to ask things like: how did metric X today compare with metric X yesterday (or on the same day last week if we adjust the AWR defaults to keep two weeks of data); how did metric Y look different around 3:00 pm today when the users were complaining about the performance.